In the related art, different hand pieces for the most different dermatological treatments with light have become known, the hand pieces being equipped with different means for beam shaping, depending on the particular treatment. Thus, for example, hand pieces for performing the so-called “non-contact technique” are known, in which an optical path which, at least partially, runs in the open atmosphere, is applied to the skin. The optical path is shaped through optics which are also used to influence, for example, to homogenize the intensity distribution within the cross-section of the beam. The optics have a surface which emits the light and is not in contact with the skin during the treatment; the desired spot diameter at the treatment site is changed by varying the distance between the emitting surface and the skin surface, utilizing the radiation divergence.
Another method is known as contact technique in which a transparent optical medium, through which light is passed, is placed onto the skin with its light exit surface. By placing the light exit surface onto the skin, an adaptation of the index to the skin is accomplished, thus preventing that a large part of the energy is scattered back from the skin and is therefore not available for the application.
A hand piece of that kind is connected to a laser radiation source via a light guide device which is so flexible that the hand piece is relatively freely movable, thus allowing the operator to easily direct the laser beam onto the treatment area. Arranged inside the hand piece downstream of the light guiding device is an optical element which is composed, for example, of quartz or of sapphire and features a light entrance surface and a light exit surface that is to be placed onto the skin.
In this context, above all, the relatively large loss of optical power of up to 30% constitutes a disadvantage. The heat loss arising in the process causes problems which, if at all, can only be solved by complex structural measures since dermatological treatments require electromagnetic radiations of relatively high energy.
For the latter reason, as a rule, one endeavors to keep the optical transmission path for the radiation as short as possible, in particular, inside the hand piece. An option in this respect is to integrate the radiation source into the hand piece which, however, results in the disadvantage that the hand piece becomes relatively large and heavy. In this context, the increase in weight is caused, not least, by the measures which are required for cooling. In the case of an integrated radiation source, moreover, it is required for the hand piece to be supplied via power supply and control lines as a result of which its handling is hampered to an unwanted degree.
When diodes are used as laser radiation source in a weight-saving manner and integrated into the hand piece, the disadvantageous effect is produced that the individual laser bars produced by the laser diodes are imaged onto the treatment site and thus homogeneous irradiation of the skin area to be treated is not guaranteed. In this context, it is neither possible to accomplish the desired spot sizes by simply changing an optical element as, for example, by replacing the quartz or the sapphire block in the case of the thermal light source since these are not used here.
An alternative option to the integrated radiation source is to generate the electromagnetic radiation in a separate radiation source which is set apart from the hand piece, and to connect the radiation source to the hand piece via a light guide device. Possible light guide devices include liquid light guides or also bundles of solid light guides. Such light guide devices have the advantage that they can pick up light at a large angle and that they are still flexible even in the case of a relatively large cross-section, allowing nearly unhindered alignment of the hand piece with the skin section to be treated.
Due to the large numerical aperture of such light guides, however, the radiation exits these light guides at very large angles (typically 67° to 80°). In the case of such a large angle of radiation, it is difficult to produce different defined spot sizes having diameters in the range approximately from 5 to 20 mm at the application site because in order to vary the diameter, the distance between the emission-side end of the light guide device and the skin has to be changed in a range of only a few millimeters.
Moreover, not only the spot size but also the intensity distribution within the beam cross-section change very quickly as the distance of the emission-side end from the skin increases. For example, if a light guide has a favorable ratio between diameter and length, a beam profile in the form of a flat top is present at its output. However, this becomes a Gaussian distribution as the distance from the emission surface increases. If the intensity is distributed inhomogeneously over the beam cross-section, overtreatments or undertreatments may result within the treated skin area.